1. Field of the Invention
The present invention relates to a plastic composition on the basis of a vinylhalide or a vinylidene halide polymer or copolymer, more particularly substantially plasticizer free polyvinylchloride, containing usual additives, such as stabilizers and/or lubricating agents.
2. Description of the Prior Art
Plastic compositions of this type on the basis of a vinylchloride or vinylidene chloride polymer or copolymer composition, are known in the art.
In processing plastic compositions on the basis of thermoplastics, more particularly hard polyvinylchloride, problems may occur, depending upon the type of additives, such as stabilizers, lubricants, pigments and the like and fillers, such as chalk, kaolin, calcium salts, asbestos etc. These problems are inherent with the fact that the thermoplastic mass including additives and fillers, may tend to adhere to the metal surfaces of molding tools of the extruders, viz the extrusion nozzles, due to which deposits of additives and/or partially decomposed polymers will be formed upon said metal surfaces, which deposits will give rise to undesired changes in the surface of the product to be extruded such as webs, sheets, pipes, foils and the like. This phenomenon is known in practice as a so-called deposit of additives, or plate out. Said plate out therefore concerns a deposit of agents from a plastic composition at the time of extruding certain products. Said plate out may even so hamper the flow velocity of the composition to be processed through the extrusion nozzles, that the shape of the final product will no longer be correct.
From the above it follows, that in actual practice it is essential to interrupt the extrusion when such deposits occur upon metal surfaces of the molding tools of the extruders, at the time when changes are observed in the surface of the products being extruded, in order to remove said deposits or plate out. Consequently both a temporary stop of the production and considerable losses of material will be involved.
Naturally, plastic pipes showing scratches at their outsides or their insides cannot possibly be delivered, as in that case said scratches will decrease the mechanical properties of the pipes, and will also cause these pipes not to be accepted by purchasers.
This also holds for plastic foil, produced on calender rollers.
Efforts have been made to alleviate said plate out by including silane additives in the respective compositions but said additives have not proved to be sufficiently effective.
The latter also results from the fact that the deposits, generally called plate out, as described hereinbefore, strongly depend on the type of vinylchloride polymer, or vinylidene chloride polymer as used.
The deposit phenomenon particularly occurs when polyvinylchloride is employed, obtained by suspension polymerization, whilst no deposits or plate out or almost no deposits or plate out will occur when a polyvinylchloride is employed, obtained by emulsion polymerization.